In this paper, we developed a new 3D-printing system for magnetic elastomer, and demonstrated to fabricate artificial cilia. Natural cilia are hair-like organ found in nature. They are effective fluidic system in the natural world that are widely observed on surfaces of microorganisms of creatures, such as Paramecium and throat surface of mammals. Recently, the motion of cilia has been analyzed and mimicked for developing soft actuator, for example, some studies on artificial cilia driven magnetically have been reported. They are small soft actuators, and there are various manufacturing methods for these actuators depending on materials and products. Among them, authors have already developed the concept of a printing system that not only forms a three-dimensional object but also prints out the deformation of the structure. This system can fabricate various shapes of soft actuators without any assembly. In this report, we utilized UV-curable urethane acrylate as a more flexible material than that used in the previous reports, and fabricated artificial cilia by the printer. We set magnetic anisotropy to each cilium and mimicked a metachronal wave, sequential action of plural cilia that causes effective flow.
Yttria-stabilized zirconia (YSZ) has been used for an electrolyte of solid oxide fuel cells (SOFC). To enhance the efficiency of SOFC, we developed a corrugated, or wavy-shaped, YSZ sheet for the electrolyte. As the corrugated sheet has larger surface area than a flat-type sheet, higher energy density can be obtained. We have proposed micro powder imprint (μPI) with multi-layer imprint process to fabricate micro scale pattern on the both surfaces of a thin YSZ sheet. The μPI is a combined process of nano imprint lithography and powder metallurgy; the resolution is high, and the process is mass-productive. In this work, we selected a compound material containing YSZ powder and a binder consisting of thermoplastic resin as a starting material. The compound sheet was prepared by tape casting from slurry and was imprinted by a fine-patterned mold with stacked on a silicone rubber sheet. The silicone rubber was so flexible that micro patterns on the both sides of the compound sheet was obtained after imprint. In the present work, the process condition of μPI and the heat program of debinding and sintering were also considered. As a result, a wave-type sintered YSZ sheet without significant defects was successfully obtained.
Solid oxide fuel cells (SOFCs) are fuel cells made of ceramics. To increase the SOFC energy density, we developed an SOFC with a wavy electrolyte layer. As a wavy electrolyte has a larger reaction surface area than a flat electrolyte, a higher energy density could be obtained. Our proposed process is named micro-powder imprint (µPI) with a multilayer imprint process that is useful for fabricating a microscale pattern on a ceramic sheet such as an SOFC electrolyte layer. µPI is based on nanoimprint lithography; therefore, it also exhibits the same advantages of high resolution and mass productivity. The starting material for µPI is a compound sheet containing ceramic powder and binder materials consisting of thermoplastic resin. In this study, two different sheets were stacked into one sheet as a multilayer sheet for the µPI process to form a wavy compound sheet. As the initial state of the stacked sheet, including the mechanical properties of each layer, affects the final wavy shape, we changed the material composition. As a result, the SOFCs unit cell with a wavy electrolyte was fabricated. Note that the anode layer was formed at the same time. After adding the cathode layer, we succeeded in preparing a complete cell for testing power generation.
In this study, a micro patterning process is proposed and developed in order to obtain various functional properties on the surface of an object. Nano imprint lithography (NIL) has recently been the focus of much attention, because of advantages such as high accuracy, low cost, and ease of operation. However, problems can occur during demolding when using this method, such as the destruction of high-aspect patterns during the process. It is also, almost impossible to form an over-hanging pattern. In order to overcome these problems, we propose a multi-step imprinting process with an in-plane compression method. A hierarchical multi-scale pattern can be produced using multi-step imprinting, and the aspect ratio of the imprinted pattern can be increased by using the in-plane compression method. A hierarchical multi-scale pattern with a high aspect ratio was produced by combining the two methods. The effectiveness of the proposed method is demonstrated by the results of the experimentation.
Biomimetics is a field of technologies based on imitating the functions and properties found in living organisms. The application of the super-water-repellent fine structure of lotus leaves to create waterproof products is a well-known example of biomimetics. The present study examined the surface structure of snail shells, which exhibit oleophobic properties oil repellency and explored the feasibility of recreating this structure on the inner surfaces of conventional biliary stents. Observations of snail shells under an electron microscope show a covering of extremely fine protrusions of around 200 nm in size. When water enters the pores between these fine protrusions, a film of water exhibiting supernanohydrophilic structure forms on the shell. Because water and oil are immiscible, this film repels oil. We would expect stent occlusion to be less likely with a biliary stent having this structure on its inner surface. Biliary stricture caused by bile duct cancer or bile duct obstruction can lead to icterus and may, in serious cases, induce fatal hepatic failure. A surgical procedure that places indwelling biliary stents inside the biliary tract is sometimes performed to secure a passage for bile flow. However, conventional stents are prone to occlusion due to the accumulation of biliary sludge, resulting in the need for a second surgery to replace the stent. This problem is attributable to the polyethylene used to make the biliary stents; polyethylene is susceptible to the adhesion of cholesterol and fats found in the bile, eventually leading to stent occlusions. This paper reports our efforts to develop biliary stents that feature antifouling properties inspired by biomimetics to address this problem; specifically, the development of oleophobic inner stent surfaces featuring supernanohydrophilic structures inspired by snail shell surfaces.
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